dm: cope with access beyond end of device in dm_merge_bvec

If for any reason dm_merge_bvec() is given an offset beyond the end of the
device, avoid an oops and always allow one page to be added to an empty bio.
We'll reject the I/O later after the bio is submitted.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>

1 files changed, 3 insertions, 0 deletions

diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index 469cec54f371..ace998ce59f6 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -843,6 +843,8 @@ static int dm_merge_bvec(struct request_queue *q,
                 goto out;
 
         ti = dm_table_find_target(map, bvm->bi_sector);
+        if (!dm_target_is_valid(ti))
+                goto out_table;
 
         /*
          * Find maximum amount of I/O that won't need splitting
@@ -861,6 +863,7 @@ static int dm_merge_bvec(struct request_queue *q,
         if (max_size && ti->type->merge)
                 max_size = ti->type->merge(ti, bvm, biovec, max_size);
 
+out_table:
         dm_table_put(map);
 
 out: